Preeclampsia is a hypertensive disease of late pregnancy and is a major cause of maternal and fetal mortality and morbidity. Five to ten percent of all pregnancies and up to 20 percent of primagravidas are affected yearly in the United States. The only curative treatment for this syndrome is early delivery, resulting in many neonatal complications due to prematurity. Recently several laboratories have documented low levels of prostacyclin (PG12) and/or elevated levels of thromboxane A2 (TxA2) 1-5. Similar results have been seen in this disease in an ovine model of preeclampsia, and beneficial, effects of thromboxane synthetase inhibitors have been reported in the ovine model. However, the effects of thromboxine synthetase inhibitors have not been studied in gravid primates. The purpose of this study is to determine the effects of CGS 12970, 3-menthyl-2 (3-pyrodyl)-l-idoleoctanoic acid, a thromboxane synthetase inhibitor, in gravid nonhuman primates (rhesus).